Neutralizing transformers



July 1, 1969 G. Y. R. ALLEN 'NEUTRALIZINQ TRANSFORMERS Original Filed Oct. 22, 1965 TERMINALS s L A N M On E FREQUENCY RECEIVER POWER STATIQN 8,000 was 7,000 vous 6.000 vou FIG 2 United States Patent ABSTRACT OF THE DISCLOSURE A neutralizing transformer formed of coaxial cable wound around a magnetic core. The transformer is used 1n power stations to apply a potential to protector blocks equal and opposite to that caused by power circuit faults.

This application is a continuation of patent application Ser. No. 500,736, filed Oct. 22 1965, and now abandoned.

My invention relates to a new method of construction of transformers and especially multi-circuit neutralizing transformers. This invention relates particularly to neutralizing transformers using a video pair cable which is essentially a twisted, spaced pair of conductors with an outer shield similar to a coaxial cable. Use of such conductors gives rise to special problems which admit to new solutions.

It is the object of this invention to provide a transformer which is more compact and less expensive to manufacture than those previously used.

It is the further object of this invention to provide a transformer wherein there is little coupling loss between primary and secondary windings.

It is another object of this invention to provide a transformer wherein the carrying cable may be wrapped directly onto the transformer rather than using special windings to serve this purpose and the cable shields may be used as a primary winding for the conductors within them which will act as secondary windings.

It is another object of this invention to provide a very close coupling between primary and secondary of the transformer.

It is an object of this invention to use the shielding of a video pair or coaxial cable in a transformer for shielding of high frequency circuits carried on the video pair plus acting as a primary winding carrying low frequency currents.

It is an object of this invention to permit transmissions of frequencies up into the megacycle range but still have the same impedance as the matching or feeding cable.

These and other objects of our invention will become apparent upon further reading of the specification and drawings in which:

FIG. 1 is a schematic illustration showing a neutralizing transformer constructed in accordance with the principles of this invention; and

FIG. 2 is a schematic illustration showing a multicircuit system employing the invention.

Throughout this specification the term coax or coaxial cable shall be understood to include single or multipair video pairs as well as other types of shielded cables or wires.

Up to this time multi-circuit neutralizing transformers have been built using unshielded cables wherein the primary is wound in parallel with the secondary windings and also in close proximity or wound over the secondary windings in order to achieve the necessary degree of coupling for power transmission from the primary to the several secondaries. This has resulted in a somewhat 3,453,494 Patented July 1, 1969 bulky transformer due to the numbers of wires necessary. Further, the apparatus is quite heavy and winding problems are encountered in winding a single primary and many secondaries in close proximity.

Another problem in current transformer construction is the matching of impedances. For maximum transmission of energy the impedances on one side of the transformer must be equal to those on the other side of the transformer.

Further in winding transformers for use at high frequency, considerable energy is lost through flux leakage. Thus, leakage comes about in flux transmission between the primary and secondary of the transformer. This problem becomes more serious at high frequencies than at low frequencies.

It is common practice in the transmission of energy and signals of frequency for any distance to use coaxial cables and video pair type cables as they give a standard impedance and avoid interference from sources extraneous to the equipment.

The construction of this transformer is as follows:

Coaxial cable is wound in layers about a central core of magnetic material. Examples of the coaxial cable which may be used are either of the straight or twisted video pair type.

A transformer according to this invention is shown in FIGURE 1 where the coaxial cable is wound about a core appropriate and the two ends of the coaxial cable are attached to terminals 12, 13 and 14.

As shown in this embodiment a coaxial cable 10 is wound in the usual fashion about a core 11. The conductors 5 of the cable are each attached to terminals 12 and 13 at each end of the conductor and the shield 7 is attached to a terminal 14 at each end.

It is understood that a multi-pair cable or a multiplicity of coax cables wound in similar fashion are within the scope of this invention. In such a cable the shields should be connected together to a separate terminal at both input and output of the transformer. Further, the shields may be connected to any one of the several terminals as the situation demands.

This transformer can be used as a multi-circuit neutralizing transformer at any point along a coaxial cable and such use is shown in FIGURE 2. A coaxial cable is shown connected between a frequency source 15 and a frequency receiver 16. In general terms the operation of the transformer in FIGURE 2 is as follows:

Due to a power circuit fault to ground a current will flow through the power station grounding circuit 17 and to ground thus raising the potential at the power station as compared to a distant point. This potential will trip the protector blocks 18 and possibly damage the equipment by a permanent ground or in some other way. If a neutralizing transformer is inserted into the circuit with the secondary windings connected in series with the conductors 5 of the coaxial cable 10 as shown at 19 in FIG- URE 2, the high potential will be applied to primary winding 20 and the resulting current flow will induce an equal and opposite potential on the secondary windings 21. Thus under ideal conditions an equal and opposite potential will be applied on the ground side and on the conductor side of the protector blocks. Thus the neutralizing transformer applies a potential across the protector blocks equal and opposite to the potential applied by the ground to the protector blocks. Thus the ground leak and resulting potential will not affect the operation of the coaxial cable.

In those applications where coaxial cable is used the coaxial cable 10 extends between a frequency source 15 and a frequency receiver 16. The twisted pair of conductors 5 may be subject to voltage of 8,000 volts more or less from a power circuitfault to ground. In the absence of a neutralizing transformer a high potential will be built up between the source and the receiver with possible damage to the circuit and its protectors.

By using a neutralizing transformer as shown in FIG- URE 2 damage to the circuit will be avoided. The transformer 19 may be wound as shown in FIGURE 1.

In the embodiment shown the coaxial cable conductor 6 will be connected to the respective terminals of the neutralizing transformer and a ground Wire 8 will be connected to the shield of the coaxial cable winding. The shield of the coaxial cable 10* may be used as a ground wire under suitable conditions and in this case the shield of the coaxial cable would be connected to the shield of the coaxial cable Winding which acts as the primary of the transformer.

Another situation in which a neutralizing transformer is used is when a cable, such as telephone cable, has voltage induced on it. For example, where a multi-grounded neutral power system has a ground return through an area of very high ground resistance and has a mean return path of 1 to 1 /2 miles below the surface of the earth. Here a cable passing nearby will have a voltage induced into it.

However, because of shielding factor the voltage induced into the conductors of the shielded cable will be somewhatless than that induced into the shield of the same cable. Thus, when a neutralizing transformer is connected into this system and the potential from the sheath is used to excite the transformer primary, then the voltage generated across the secondary will be greater than the voltage which it is intended to neutralize.

This result can be avoided by spacing the primary winding from the secondary winding to allow a leakage just sufficient to cause the generated voltage to balance the induced voltage rather than overbalance it. Spacing between the primary and secondary can be accomplished by varying distance between the shield of the transformer cable and the internal conductor or if a conventionally wound transformer is used varying the space between the primary and secondary winding.

That which is claimed is:

1. In combination, a neutralizing transformer circuit for use with a coaxial cable having a plurality of spaced electrical conductors surrounded by a conductive sheath means, a protector block means connected in series with said spaced electrical conductor means, said conductive sheath means of said cable being connected to ground to form a ground conductor and the extremities of said spaced conductors being connected to different electrical potentials, a transformer having a winding of coaxial cable wound in layers about a magnetic core, said transformer coaxial cable having a sheath means connected in series with said ground conductor and forming the primary of said transformer, and a corresponding plurality of electrical conductors of said transformer coaxial cable connected in series with said plurality of spaced electrical conductors and forming the secondary of said transformer.

2. In combination, a neutralizing transformer circuit for use with a coaxial cable having a plurality of spaced electrical conductor means surrounded by a conductive sheath means, a protective block means connected in series with said spaced electrical conductor means, said conductive sheath means being connected to ground to form a ground conductor and the extremities of said spaced conductor means being connected to a frequency responsive means, a transformer having a winding of a coaxial cable wound in layers about a magnetic core, said transformer coaxial cable having a sheath means connected in series with said ground conductor and forming the primary of said transformer, and a corresponding plurality of electrical conductors of said transformer coaxial cable winding being connected in series with said plurality of spaced electrical conductor means and forming the secondary of said transformer.

3. In combination, a neutralizing transformer circuit for use with a coaxial cable having a plurality of spaced electrical conductors surrounded by a conductive sheath means, the extremities of said electrical spaced conductors being connected to a frequency responsive means, a ground wire connected in electrical parallel with said sheath means and connected at one of its extremities to ground to form a ground conductor, a transformer having a winding of coaxial cable wound in layers about a magnetic core, said transformer coaxial cable having a sheath means connected in series with the other extremity of said ground conductor and forming the primary of said transformer, and a corresponding plurality of electrical conductors of said transformer coaxial cable connected in series with said plurality of spaced electrical conductors and forming the secondary of said transformer.

References Cited UNITED STATES PATENTS 7/1965 Crom 31718 OTHER REFERENCES LEE T. HIX, Primary Examiner.

A. D. PELLINEN, Assistant Examiner.

US. Cl. X.R. 

